1,This is the best one of machines that ----in working order.A is.B are C were D was参考答案是b

1,This is the best one of machines that ----in working order.A is.B are C were D was参考答案是b
1,This is the best one of machines that ----in working order.A is.B are C were D was
参考答案是b

1,This is the best one of machines that ----in working order.A is.B are C were D was参考答案是b
选择A
注意前面的时态是现在时
而且这句话的翻译是：这个机器是所有机器中运转最好的一个.凭借常识也应该是现在时,通过前面的is 可看出是单数.

A

A